Process for the catalytic production of hydroxyl-ammonium salts

ABSTRACT

Improvement in the process of reacting nitric oxide and hydrogen in an acid reaction medium in the presence of a catalyst of the platinum group which is suspended on graphite, active carbon or a mixture thereof wherein the process is carried out in the presence of carbon dioxide to improve the selectivity of the catalyst for hydroxyl ammonium salt production.

United States Patent [151 3,655,336 Heine [4 1 Apr. 11, 1972 [54] PROCESS FOR THE CATALYTIC [56] References Cited g g l lv gggl U la ggl j Tg UNITED STATES PATENTS 3,133,790 5/1964 Jockers ..23/l90 A [72] Inventor: Heinz Heine, Krefeld, Germany FOREIGN PATENT OR PPUCA IONS [73] Assignee: Farbenfabriken Bayer Aktiengesellschaft, S A T Levefkusen Germany France [22] Filed: 1969 Primary Examiner-Oscar R. Vertiz LN 667 8 Assistant Examiner-H. S. Miller [211 App 0 8 1 Attorney-Connolly and Hutz Foreign Application Priority Data [5 7] ABSTRACT Nov. 2, 1968 Germany ..P 1806 537.7 Improvement in the process of reacting nitric oxide and hydrogen in an acid reaction medium in the presence of a [5 2] US. Cl ..23/117, 23/ A catalyst of the platinum group which is suspended on graphite, [51] Int. Cl. ..C0lg 1/10, COlc 1/28 active carbon or a mixture thereof wherein the process is car- [58] Field of Search ..23/ 190 A, 117 ried o t in the presence of carbon dioxide to improve the selectivity of the catalyst for hydroxyl ammonium salt production.

3 Claims, N0 Drawings The present invention relates to a process for the catalytic the form'of cascades. Carbon dioxide is preferably added to the synthesis gas but may be introduced separately into the reaction vessels. The carbon dioxide may also be supplied in the form of carbonates or carbaminates.

production of hydroxyl-ammonium salts from nitri oxide a d 5 The process will be explained more fully below with the aid hydrogen in acid solution, which is characterized inthat the Ofthe mP reaction takes place in the presence of carbon dioxide.

It is known that hydrogen and nitric oxide can be reacted in EXAMPLE 1 an acid medium noble metal catalysts to Produce y y 30 g. of a platinum/graphite catalyst containing approxiammonium 5915 (German Patent Specification 968,363 mately 1 percent of platinum were added to l l. of a 4NH SO and German Auslegeschrifi 8 1,177,118); Side by Side with solution, and a-mixture of 10 to 12 liters of nitric oxide per this y occur the formauon of ammomum Sulphate and hour with double the quantity of hydrogen was introduced nitrous Oxide- Various Proposals have been made to suppress with stirring at 40 to 45 C. The catalyst was filtered off after the reaction which leads to ammonium sulphate, for example 15 gh and was used again f r the ddi i f f h h the use of lead, mercury, sulphur or selenium for sel ric acid. No CO was added to the synthesis gas during the first catalyst Polsonmg (German pafem Speclficanon 945,752 two passes in this example whilst in the last two passes approxand 956,038) puFtherfnore been found that Farbon imately 2 percent of CO was added. The following conversion monoxide or formic acid but not higher carboxylic acids can rates were achieved. be used for the same purpose (Belgian Patent specification No. 692,976).

On further investigation into the optimum conditions for CO o Con ion preparing hydroxylamine, it was surprisingly found that cartent f 1 to fi fi Comer. bon dioxide is an effective agent for improving selectivity in synthegis i 2 332 5 2128 selectivity the synthesis of hydroxylammonium sulphate from nitric oxide 2 5 perc ent perc ent percent percent ercent and hydrogen. This was all the less to be expected since car- Passes: bon dioxide is used in many reactions as an inert gas. It has the 1 0 0 20 9 22 advantage over carbon monoxide mentioned above of trouble- 3: 1 g u g 3; free dosing since it does not cause inactivation of the catalyst LII: 2:0 9:8 75 1 84 even when used in considerable quantities. It is more 0 economical than formic acid. The minimum concentration depends on various factors. According to our experience, one may proceed on the basis that optimum results are achieved if the active centres of the catalyst are modified with carbon dioxide in the required sense, i.e. with a view to maximum hydroxylamine formation.

It is therefore first of all necessary to ensure a sufficient concentration of CO in order to obtain the completest possible occupation of the active centres of the catalyst. As the reaction continues, it is then only necessary to supply further CO in sufficient quantity to maintain the required occupation of the catalyst. If the reaction is carried out in an acid pH range, extremely small quantities of CO practically at the limit of detectability, are sufiicient. The concentrations of CO to be employed thus depend largely on the reaction conditions. In a reactor equipped with a stirrer, for example, part of the waste gas is continuously returned by suction and recycled; the effective Co content in the reaction gas thereby becomes greater than the value adjusted in the synthesis gas.

Optimum results were achieved with CO concentrations in the synthesis gas of about 0.01 to 2 volumes per cent. Larger quantities are unnecessary and therefore uneconomical whereas, with substantially smaller quantities, the desired modification of the catalyst is achieved only after the synthesis has been carried out for a considerable time.

The process is otherwise carried out under the conditions known from the prior art, e.g. US. Pat. specification Nos. 2,628,889 and 3,406,011; the reaction takes place in solution in a mineral acid, preferably sulphuric acid, in which the catalyst material platinum, palladium, rhodium, iridium, ruthenium and alloys thereof, preferably platinum, suspended on graphite or active carbon. The reaction is carried out in stirrer vessels which may be arranged singly or in series or in The vaifi cm conversion rate are based on the amount of nitric oxide put into the process. The selectivity is defined as 100 times the ratio of mols of hydroxylammonium sulphate formed to the sum of hydroxyl-ammonium salt, ammonium salt and N 0 formed.

The addition of carbon dioxide becomes noticeable especially towards the end of each reaction period. This is shown by the progress in conversion to In ;Q C for two of the above mentioned reaction periods at intervals'of 2 hours:

2nd pass (WllhOUtCUz) C =0; l; l; 20

4th pass (withCO c,,,5(% =0; 1; 1; 2

The addition of carbon dioxide is therefore of interest especially for continuous synthesis in which the acid originally added to the reaction solution is used as far as possible.

EXAMPLE 2 25 g. of a platinum/graphite catalyst containing approximately 1 percent of platinum were added to l l. of 4N H and a mixture of 10 to 12 l. of nitric oxide with approximately 1.7 times its quantity of hydrogen was introduced with stirring at approximately 40 C. The catalyst was filtered off after 8 hours and used again after the addition of fresh H 80 The nitric oxide used for this experiment was treated either with purified river water or with NaOH in a scrubbing tower. Gas scrubbed with NaOH was free from CO but treating the gas with river water was a convenient way of adding small quantities of CO which was dissolved in the river water.

Analysis to determine CO was carried out gas chromatographically in the waste gas without previous concentration. The fact that there was only a slight decrease in selectivity during the fifth pass can be explained by the fact that the N0 gas meter which was filled with water still contained dissolved residues of C from the fourth pass, which were insufiicient to be detected by gas chromatographic analysis but nevertheless were suflicient to improve the selectivity What is claimed is:

1. In the process of producing hydroxyl ammonium salt by catalytic hydrogenation of nitric oxide in a sulphuric acid medium with a catalyst of the platinum group suspended on graphite, active carbon or a mixture thereof, the improvement for increasing the selectivity of said catalyst for the production. 

2. The process of claim 1 wherein a carbon dioxide containing synthesis gas is employed.
 3. The process of claim 2 wherein said synthesis gas contains CO2 in an amount of from about 0.01 to 2 percent by volume. 